This invention relates to an injection molding unit forming part of an injection molding machine for synthetic materials and is of the type which includes a plasticizing unit replaceable by program control. The plasticizing unit includes a plasticizing cylinder which receives a rotatable and axially shiftable feed screw, a supply block which has a central passage for receiving the plasticizing cylinder and through which the synthetic material is delivered to the plasticizing cylinder by means of a supply conduit from a reservoir situated externally of the injection molding unit. The supply conduit is connectable to a hopper provided in the supply block. The injection molding unit is further equipped with at least one hydraulic drive cylinder for inserting the injection molding unit in the injection mold assembly and a hydraulic injection cylinder for causing the feed screw to perform its injection stroke by virtue of an axial shift within the plasticizing cylinder. Further, there are provided radially guided bolts for a releasable locking of the plasticizing unit with the other components of the injection molding unit with the intermediary of the supply block.
A known injection molding unit of the above-outlined type is disclosed in published European Patent Application No. 69,221 and German Offenlegungsschrift (non-examined published application) No. 3,229,223. In the structure disclosed therein the plasticizing cylinder and the supply block are unreleasably attached to one another and form a relatively bulky and heavy structural unit. The latter is, as a plasticizing unit in a broad sense, releasably lockable to the other components of the injection molding unit as a precondition for its replaceability. For effecting locking, the supply block may be axially tightened to the housing of the other components of the injection molding unit with the aid of clamping bolts which have obliquely oriented faces and which are guided for radial movement in the housing. Consequently, for replacing the plasticizing unit, in each instance it is necessary to disassemble from the supply block the supply device which advances the plastic material to be processed by the plasticizing unit. Such a work could be included only with a very significant technical input in the program of a computer associated with the injection molding machine.
In contradistinction, in an apparatus disclosed in German Patent No. 3,228,161 the type, number and sequence of materials may be included in the program of the computer for selectively charging the hopper or chute of the supply block with different types of material. The plastic material changing device includes a rail secured to the supply block and oriented horizontally and transversely to the injection axis and extending on both sides of the hopper. The device further has a motor-driven sled mounted on the rail and reservoirs which are secured to the sled and which accommodate the various plastic materials. The reservoirs may be displaced with the sled on the rail in such a manner according to the program that the outlet opening of the supply container accommodating the momentarily desired plastic material is aligned with the hopper of the supply block and between the outlet opening of the reservoir and the hopper an open connection exists by virtue of a drop hole of the rail. It is a disadvantage of this arrangement that during the setting of the injection molding unit onto and its removal from the injection mold assembly, at the reservoirs significant tilting torques appear which expose the sled, its guide components, as well as the runner rail to significant loads.
As disclosed in German Offenlegungsschrift No. 3,337,546 and German Patent No. 904,463, it is also known to integrate in the injection molding machine two or more injection molding units which are selectively placed intc the working position to process different plastic materials with different plasticizing units with only short down periods. To provide for the alternating use of plastic materials and plasticizing units by means of entire injection molding units in a standby state is inherently very complex and expensive.